The atomic force microscope (AFM) or scanning force microscope (SFM) is a very high-resolution type of scanning probe microscope, with demonstrated resolution of less than one nanometer, more than 1,000 times better than the diffraction limit of optical microscopy. An AFM typically consists of a microscale cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. The cantilever is typically silicon or silicon nitride with a tip radius of curvature on the order of nanometers. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever according to Hooke's law. Depending on the situation, forces that are measured in AFM include mechanical contact forces or Van der Waals forces, capillary forces, chemical bonding, electrostatic forces, magnetic forces, Casimir forces, and salvation forces.
Generally, atomic sharpness of probe's apex is required to achieve needed nanometer resolution using the AFM. Nanometer resolution is typically needed for surface roughness measurements and accurate gate critical dimension (CD) and sidewall profile metrology for advanced semiconductor devices. Typically, flared Si and so-called “tripod” probes can be used by the CD AFM. However, such probes generally have a radius of apex curvature equal or exceeding 5 nm, placing a limit on CD AFM resolution. Various sharp ridge AFM probe characterizers typically have the same problem, a radius of curvature of about 5 nm. One method to provide atomically sharp AFM probes has been to place the probes in an Field Emission/Ion Microscope (FIM) to characterize and sharpen existing probe tips prior to their installation in the AFM.
However, even when atomically sharp AFM probes are provided, their continued use can result in wear or contamination of the probe tip, resulting in loss of resolution. Additionally, the sharpened AFM probes can inadvertently come into unwanted contact with a sample surface during probing or calibration, also resulting in damage and/or contamination. In either case, the probe tip can become inadequate for providing useful AFM images. Consequently, AFM probe tips are typically considered disposable, resulting in increased costs of operation for the AFM. Additionally, because AFM probes typically need to be replaced frequently, an AFM can be frequently offline for replacement and recalibration of the AFM with the new probe. Therefore, there exists a need for improving the lifetime of AFM probes.